A class of ceramics has now been discovered that has the ability to superconduct electricity at liquid nitrogen temperatures (77.degree. Kelvin). This ability to superconduct electricity at liquid nitrogen temperatures is a considerable improvement over the more conventional metallic alloys that superconduct at liquid helium temperatures (4.degree. Kelvin). These ceramic materials, as a consequence of being brittle, are difficult to process into fine, twisted and wound filaments that are needed for the magnets that are used in electrical motors and generators. To prevent the violent failure of these magnets, the ceramic filaments must be mated or coated with normally conducting metals, without contaminating the ceramic materials, must be of a small diameter, typically 4 to 4000.times.10.sup.-6 m, and must be twisted or braided into strands. Then, these strands in turn are twisted or braided together to make the cables which are then wound into the configuration of the desired magnet.
The superconducting filaments currently used involve the mating of superconducting metal to a normal conducting metal to prevent the violent destruction of a finished product, such as a magnet. The methods currently used to produce all metal superconducting filaments depend on the ductility inherent in the type of metal used, usually an alloy of niobium and titanium. The ductility allows the extrusion of fine filaments usually by inserting the superconducting metal into a tube of normal conducting metal and drawing the composite down into a fine filament. These methods are not successful when the superconductor material is a ceramic due to their brittleness.
The following U.S. patents illustrate some current methods of bonding a metal component to a solid ceramic substrate for state of the art utilization:
Arno Neidig et al in U.S. Pat. No. 4,591,401 illustrates a process for directly bonding a metal component, the surface of which is covered by an oxide layer after preoxidation, to a solid ceramic substrate, which comprises placing the metal component covered by an oxide layer on the solid ceramic substrate, heating the solid ceramic substrate with the metal component placed thereon to a temperature above the eutectic point of the metal and metal oxide but below the melting point of the metal, the combination therewith of forming parallel grooves, before said preoxidation on the surface of the metal component which is to be bonded to the solid ceramic substrate, and then effecting the heating to make the metal ceramic bond.
Another U.S. Pat. No. 4,470,537 illustrates the bonding of a solid piece of ceramic to a solid piece of metal by heating under pressure to a temperature below the melting point of both the metal and the ceramic for the purpose of increasing the strength of the bonded metal/ceramic structure. Zirconium metal is illustrated with silicon nitride being the ceramic material. The process may also be used for producing a ceramic material-to-ceramic material bonded by bonding two ceramic parts to a metal part therebetween.
The following articles illustrate the now considered common superconducting ceramic materials and their potential end use:
1. "Superconductors" in Materials at Low Temperatures, Section 13, by Ekin, J. W., The American Society, Metals Park, Ohio (1983).
2. Z. Phys. B--Condensed Matter, 64, 189-193 by Bednorz, J. G. and Muller, K. A. (IBM Zurich Research Laboratory, Ruschlikon, Switzerland) (1986).
3. Physical Review Letters, Volume 58, Number 9, 908-910 by M. K. Wu et al and P. H. Hor et al, (1987).
The present invention overcomes the inherent brittleness problem with the superconductor material when it is a ceramic by using a direct method to bond superconducting ceramic materials directly to the normal conducting metal.